Crankshaft balance weights and method of assembly

ABSTRACT

A crankshaft is formed with stub web portions for attachment of balance weights. The crankshaft bearing surfaces are ground and then the weights are electron beam welded to the web portions, which have a stepped configuration to enable indexing for sequential weight welding. After hardening trimmer plates are fastened to the weights axially of the crankshaft to complete the balancing. This provides an inexpensive, easily machined, accurately balanced crankshaft.

United States Patent 1191 Stewart CRANKSHAFT BALANCE WEIGHTS AND METHODOF ASSEMBLY William F. Stewart,

Peterborough, England Assignee: Perkins Engines Limited,

Peterborough, England Filed: Mar. 11, 1971 Appl. No.: 123,461

Related US. Application Data Division of Ser. No. 26,922, April 9, 1970,Pat. No. 3,673,651.

Inventor:

US. Cl. 74/603, 74/597 Int. Cl. F166 3/20 Field of Search 74/603, 597

References Cited UNITED STATES PATENTS 12/1915 Fekete 74/603 2/1918Gordon 74/603 4/1918 O'Brien 74/603 1451 July 31, 1973 FOREIGN PATENTSOR APPLICATIONS 431,712 7/1935 Great Britain 74/603 431,585 7/1935 GreatBritain 74/603 Primary Examiner-Charles J. Myhre Assistant ExaminerF. D.Shoemaker Att0rneyGerhardt, Greenlee & Farris [5 7 ABSTRACT A crankshaftis formed with stub web portions for attachment of balance weights. Thecrankshaft bearing surfaces are ground and then the weights are electronbeam welded to the web portions, which have a stepped configuration toenable indexing for sequential weight welding. After hardening trimmerplates are fastened to the weights axially of the crankshaft to completethe balancing. This -provides an inexpensive, easily machined,accurately balanced crankshaft.

1 Claim, 11 Drawing Figures Patented July 31, 1973 .3 Sheets-Sheet 1Patented July 31, 1973 3,748,925

3 Sheets-Sheet 2 3 Sheets-Sheet 5 CRANKSHAFT BALANCE WEIGHTS AND METHODOF ASSEMBLY This application is a division of U. S. Pat. application No.26,922, filed Apr. 9, 1970 now US Pat. No. 3,673,651.

The present invention relates to crankshafts for engines and to a methodof making crankshafts.

Hitherto it has been the practice to use balance weights on enginecrankshafts to reduce vibration and to reduce bearing loads.

Balance weights may be formed as an integral part of the crankshaft orseparate weights may be attached after forming the crankshaft.Crankshafts for production engines for automotive and other applicationsusually undergo tests at rotational speeds well in excess of those theywould encounter during normal running of the engine. Under the testconditions the balance weights must remain firmly attached to thecrankshaft.

An advantage of the integrally formed balance weight on a crankshaft isthat there are no retention problems. There are several disadvantageshowever and amongst these are:

a. High initial die cost and short die life on the forming apparatusused.

b. Excessive engine bulk due to difficulty in making economic use of thespace available for placing the balance weight. The space between theconnecting rod and the adjacent side face of the balance weight whichoverhangs the connecting rod bearing could be occupied by balancing masswere it not for the fact that the bearing is then inaccessible forgrinding.

c. An excessively large billet is required to form the more intricateshape and more material has to be removed during subsequent forming. Inaddition, steel suitable for crankshafts has qualities not required forbalance weights for which little more than mass is required.

These disadvantages may be overcome by the use of separate balanceweights which can be attached to the crankshaft. A major disadvantage ofthis approach is retention of the balance weights at high speed.Solutions to the retention problem have hitherto been costly in terms oftime, machining accuracy, and the special standard of fixings necessary.Also a high standard of inspection is required during manufacture andfinal assembly. Balance weights may be attached by welding, but hithertoproposed welding methods have the disadvantage that heating and coolingof the crankshaft causes distortion.

According to the present invention, there is provided a method ofattaching balance weights to web portions of a crankshaft, comprisingthe steps of providing, on the balance weights and on the web portionsrespectively, mutually engageable surfaces each having at least onerectilinear dimension arranged so as to permit electron-beam weldingthroughout the locus of the said dimension in a direction which istransverse to the general plane of the associated web portion, andpositioning and electron-beam welding the balance weights successivelywith the respective surfaces in mutual engagement.

Further, according to the present invention, there is provided a methodof making a crankshaft comprising the steps of forming a crankshaft bodywith journal portions, crankpin portions and web portions, completingmachining of the body, providing primary balance weights and attachingthese to at least some of the web portions, balancing the body with theprimary balance weights attached, subjecting parts of the body tosurface hardening treatment, providing secondary balance weights ortrimmer plates of predetermined weight and dimensions, and attaching thesecondary balance weights or trimmer plates to the primary balanceweights.

Still further, according to the present invention, there is provided acrankshaft body having web portions adapted for attachment thereto ofbalance weights by means of electron-beam welding, each such web portionhaving a surface thereon with a rectilinear dimension the locus of whichis transverse to the general plane of the web portion for engagementwith a complementary surface on a balance weight, such surfaces beingdisposed in relation to one another so as to permit access to eachsurface of an electron beam during successive welding operations.

Still further, according to the present invention, there is provided acrankshaft having web portions with primary balance weights attachedthereto by means of electron-beam welding, the thickness of the primarybalance weights being such as to permit radial access to adjacentjournals or crank pins for the purpose of subjecting the journals and/orcrankpins to surface hardening treatment and/or to superfinishing.

Embodiments of the invention will now be described by way of examplewith reference to the drawings of which:

FIG. 1 is an elevation of one half of a crankshaft for a V-8 engine seenin the direction of arrow I in FIG. 2;

FIG. 2 is a plan of the crankshaft seen in the direction of arrow II inFIG. 1;

FIG. 3 is an end view of the crankshaft up to the midplane A-A as seenin the direction of arrow III in FIG.

FIG. 4 is an elevation of the crankshaft as seen in the direction ofarrow IV in FIG. 3 prior to attachment of thebalance weights which areshown in section;

FIG. 5 is an enlarged partial section of line VV in FIG. 3 on thecrankshaft local to a balance weight;

FIG. 6 is a similar view to FIG. 4 on a second embodiment;

FIGS. 7 and 8 are similar views to FIGS. 3 and 4 of a third embodiment;

FIG. 9 is a view on section IXIX in FIG. 10 of a balance weight with atrimmer plate attached;

FIG. 10 is a section on line XX in FIG. 9 showing how the trimmer plateis attached by one method;

FIG. 11 is a similar section to FIG. 10 showing how the trimmer plate isattached by a second method.

In FIGS. 1 to 6, there is shown one half of the length ofa crankshaftfor a V-8 engine. The other half is asymmetrical to the half shown inall fundamental respects and for the sake of convenience is notillustrated.

A crankshaft 1 has journals constituted by front, intermediate and midmain bearings 2, 3 and 4 respectively, and crank pins 5 and 6 situatedat displacement from each other. Webs 7, 8 and 9 flanking the front andintermediate main bearings 2 and 3 carry primary balance weights 10, 11and 12. A web 13 flanking the mid main bearing 4 has no balance weight.The web 7 and the associated balance weight 10 are heavier than theothers.

To attach the primary balance weights to the associated webs of thecrankshaft 1, flat surfaces 17, 18 and 19 on webs 7, 8 and 9 areelectron beam welded to surfaces 14, 15 and 16 respectively of primarybalance weights 10, 11 and 12 across the contiguous mating surfaces.

Each of the balance weights is carefully machined especially in relationto the distances between holes a and 10b and the placing of these holesin relation to the surface 14. The distance between the holes 10a and10b and the sizes of these holes is especially important because theyhave to match closely with corresponding holes in secondary balanceweights or trimmer plates described later herein. The reference numerals10a and 10b are used in relation to balance weights 10 and it is to beunderstood that other balance weights have similar holes formed withequal care and accuracy of position.

Reference numeral 20 denotes the electron discharge head of electronbeam welding apparatus. In FIG. 4 the surfaces 14, 15 and 16 are steppedoutwards from the crankshaft axis; likewise, the surfaces 17, 18 and 19.The discharge head is placed in the plane of surface 19 and aimed at it.Assembly proceeds as follows.

Balance weight 12 is placed in the desired position with its surface 16abutting surface 19 and the welding apparatus is energized to direct astream of electrons at the interface 16/19. This causes local meltingand fusion of the metals of the crankshaft and balance weight. Theelectron beam is caused to traverse the interface so that the whole ofthe abutting surfaces become united.

The discharge head 20 is next aligned with abutting surfaces 18 and 15and the electron beam welding apparatus is energized and traversed tounite balance weight 11 with web 8. Finally, balance weight 10 is unitedwith web 7v by the same procedure. The same attention is then given tothe corresponding three balance weights (not shown) at the other end ofthe crankshaft. Surface 18 is stepped inwards from surface 19 so thatthe former does not interfere with the beam to the latter. The beam mustbe placed on line-of-sight with the surface to be welded. Likewise,surface 17 must not mask the'beam from surface 18.

It is preferable that the two abutting surfaces overhang each otherbyreason that the boundaries of the two surfaces are not the same shapeor size. If this is not so then an undercut 23, as shown in FIG. 5, canbe provided on the balance weight to ensure an overhang. The overhangensures that any welding flash produced remains in a recess and notimeneed be spent in fettling it.

FIG. 6 shows how the surfaces 17a, 18a, 19a and 14a, 15a and 16a can becomplementarily angled to allow the discharge head 20 to be positionedso that the electron beam issuing therefrom will clear the-other webs orother obstructions.

In the embodiments shown in FIGS. l-6 the relative traversing of theelectron beam and the crankshaft is along a straight path which is achord of a circle with the axis of the crankshaft as center.

In the embodiment shown in FIGS. 7 and 8 the surfaces 17b, l8b, 19b and14b, 15b, 16b are cylindrical surfaces. They are stepped slightly toallow unobstructed access of the electron beam as in the case of FIG. 4.If the cylindrical surfaces are angles as in FIG. 6 they necessarilybecome conical surfaces and the electron discharge head has to be movedaccordingly.

FIGS. 9, 10 and 11 illustrate the secondary balance weights or trimmerplates 24 which are to be fitted to the balance weights to complete thecrankshaft, shown in FIG. 1. These preferably have the same shape as thebalance weights as seen in FIG. 3.

Two methods of attachment of the trimmer plates are illustrated in FIGS.10 and 1 1. Both these methods provide that there will be a mimimum oflocal distortion adjacent to the fastening means thereby minimizing theimposition of undesirable stresses on thefastening means.

In FIG. 10 there is shown a relatively thin trimmer plate 24 which has apair of holes 25 formed in it, at the same spacing within closetolerances as the holes 10a and 10b referred to previously. A steppedinsert 26 is fitted closely within hole 25 and is electron beam weldedto the trimmer plate 24 around the periphery of the hole 25. The insert26 is threaded internally. The hole 10a is a stepped hole the largerdiameter portion 27 being such as to receive the socket head 28 of a setscrew 29, the shank 31 of which passes through the smaller diameterportion 30 of hole 10a. A recess 32 is provided to receive the insert 26in closely fitting engagement in the manner of a dowel. The insert thusconstitutes an internally threaded dowel and two of them locate thetrimmer plate 24 against lateral movement relative to the balance weight10.

It will be understood that the electron beam welding of the insert 26 tothe trimmer plate permits accuracy of alignment of the dowel to bemaintained during the welding process, an advantage that cannot beguaranteed without expensive jigging with other forms of welding.Furthermore, the strength of the insert 26 in shear is relativelyunchanged before and after welding, it being understood that the insertis a very highly stressed part.

In FIG. 11 a relatively thicker trimmer plate 34 is shown attached tothe balance weight 10. The balance weight is drilled in exactly the samemanner as in FIG. 10 and the same reference numerals identify the sameparts. In this case, however, the insert 36 has a portion 37 which fitsclosely in the recess 32 and in a hole 38 in the trimmer plate 34. Arecess 39 in the outer side of the trimmer plate 34 receives a flange 40on the insert 36 which serves, with the set screw 29, to preventseparation of the trimmer plate from the balance weight 10. The insert36 in this case functions as a loose dowel.

An important feature of the invention is that the dowel holes on thebalance weights and trimmer plates can be formed prior to any weldingand can be relied upon to be useable as dowel locations after welding.

The method of making a crankshaft calls for the first step of machiningthe forging. Thus the main bearings 2, 3, 4, etc., crankpin bearings 5,6 etc., front and rear ends 46 etc., lightening holes 48, oilways 49 andthe surfaces 17, 18, 19 etc. are all completed to their properdimensions and finish so that the crankshaft does not have to return toany machine tool for subsequent metal removal. The next step is toelectron beam weld the balance weights in position. This does notinvolve widespread dispersal of heat in the crankshaft so that there isno distortion such as would cause a requirement for re-machining.Following this, the crankshaft is balanced. This step involves theaddition of temporary weights to the crankpins. The temporary weights inthis case compensate for part of the total out of balance. The actualbalancing is carried out in known manner by removing mass fromappropriate parts of the crankshaft.

After balancing, the crankshaft is in a state where the securing of aset of trimmer plates will place it in a desired state of balance forthe engine. Before securing the trimmer plates however, the crankshaftbearing surfaces undergo heat treatment to harden them. Depending uponthe type of heat treatment, the bearing surfaces may subsequently becleaned and polished to remove any surface deposits on the bearing. Thenthe trimmer plates are fitted and the crankshaft is complete, ready forfitting to an engine.

It is often the case that an engine is designed so that the cylinderblock can be bored to one of several alternative possible sizes to givetwo or three capacity-sizes of engines having correspondingly differentpiston weights. The crankshaftsof such engines are of the same basicdimensions and are in all respects, except balance, identical. Thepresent invention enables a basic crankshaft with balance-weights to bemade and balanced so that all that is required subsequently is to fitthe set of trimmer plates appropriate to the reciprocating mass of theengine in which the crankshaft is to be fitted. Each trimmer plate is,of course, carefully weighed and tested as to the position of its centerof gravity to ensure compatibility with its fellows in the set and withthe crankshaft.

Thus the present invention enables complete machining of the crankshaftat a time when no regard need be paid to the problem of balance weightswhich overhang the crankpins or main bearings; furthermere, noremachining is necessary following the welding of the balance weights.Also the screw-secured weights are attached with the screw axes-parallelwith the crank axis and the screws are relieved of the shear loads whichare carried by the dowels. This makes for greater safety than the use ofradial screws which have been used hitherto. Also the weight to beretained by screw means is a fraction of the total balance weightinstead of the whole of it as has been proposed hitherto.

The problem of balance weights is particularly acute with a V-8crankshaft in which each crank pin carries two connecting rods and theinvention has been described with reference to such a crankshaft. Itwill be appreciated that the invention can be used to solve similarproblems in connection with engines of different configuration.

I claim:

l. A crankshaft having web portions, primary balance weights attached tothe web portions, secondary balance weights each detachably secured to aside of one of said primary balance weights so as to overhang anadjacent journal said secondary balance weight secured to its associatedprimary balance weight by fastening means and including an insertintermediate said secondary balance weight and said fastening means foraligning said secondary balance weight relative to said primary balanceweight.

1. A crankshaft having web portions, primary balance weights attached tothe web portions, secondary balance weights each detachably secured to aside of one of said primary balance weights so as to overhang anadjacent journal said secondary balance weight secured to its associatedprimary balance weight by fastening means and including an insertintermediate said secondary balance weight and said fastening means foraligning said secondary balance weight relative to said primary balanceweight.